Anti-CD3 mAb-induced redirected cytotoxicity against B7-H3/P815

cells was higher than that against P815 in both CD4+ and CD8+ T cells (Fig. 1c). We examined OVA-specific cytotoxicity against E.G7 cells that express peptide antigens derived from OVA protein, using OT-I-derived CD8+ T cells to check details investigate whether B7-H3 on target cells up-regulated antigen-specific cytotoxicity of CD8+ T cells. B7-H3 expression on parental E.G7 and B7-H3/E.G7 cells is shown in Fig. S1. Cytotoxicity against B7-H3/E.G7 cells by freshly isolated OT-I CD8+ T cells was consistently higher than that against parental E.G7 cells (Fig. 2a). When the in vitro-sensitized OT-I CD8+ T cells were used as effectors, cytotoxicity against B7-H3/E.G7 was seen

even at lower effector : target (E : T) ratios (E : T = 1 and E : T = 5) and consistently showed higher cytotoxicity than that against parental E.G7 cells (Fig. 2b). These results indicate that tumour-associated B7-H3 enhanced antigen-specific cytotoxicity of CD8+ T cells. To investigate whether CD8+ T cells selectively lyse tumour cells that express B7-H3, different fluorochrome-labelled parental E.G7 and/or B7-H3/E.G7 cell combinations were injected into the peritoneal cavity of OT-I mice, and PEC were analysed after 24 hr by flow cytometry. In the mix of CMTMR-labelled E.G7 and CFSE-labelled E.G7 (1 : 2) (A-mix; i) cells, the ratio of recovered CFSE-labelled cells : CMTMR-labelled cells was approximately 2 (Fig. 2c). ZD1839 This was similar to the injected cell ratio, suggesting that the respective fluorochrome-labelled E.G7 cells were lysed equally. In contrast, for the mix of CMTMR-labelled Selleck GDC-0068 E.G7 and CFSE-labelled B7-H3/E.G7 (1 : 2) (B-mix; ii), the ratio of CFSE-labelled B7-H3/E.G7 to CMTMR-labelled WT E.G7 was dramatically reduced (Fig. 2c; centre and right panels), suggesting a selective deletion of B7-H3/E.G7 cells. Similar experiments with different fluorescent protein-expressing J588L and B7-H3/J558L cells injected into syngeneic mice also showed the selective elimination of B7-H3/J558L at 14 days (data not shown). The

selective elimination of the B7-H3-expressing target cells suggests preferential activation of CD8+ T cells in the interactions with CD8+ T cells and B7-H3-expressing tumour cells. We next examined whether B7-H3 on tumour cells enhances CD8+ T-cell activation at either the induction or effector phases using two different models. B6 and OT-I mice were sensitized in vivo with P815 or B7-H3/P815 cells as alloantigen-expressing cells and E.G7 or B7-H3/E.G7 cells as OVA-peptide-expressing cells, respectively, and then cytotoxicity against parental tumour cells was analysed. The in vivo sensitization with either alloantigen or OVA antigen by B7-H3-expressing tumour cells did not affect the induced cytotoxicity (Fig. 3a). These results suggest that B7-H3 expressed on tumour cells did not enhance antigen-specific priming of CD8+ T cells in the induction phase.